1. Field of the Invention
The present invention relates to an improvement of kneading rotors, particularly intermeshing type rotors, in a closed type kneader used for kneading mainly rubber and plastic materials.
2. Description of Related Art
As known, a closed type kneader such as a batch type kneader suitable for kneading such high polymers as rubbers and plastics, is an indispensable mechanical equipment in the rubber industry, such as in the production of tires. Requirements for this type of kneader involve high dispersion of additives into a main material and a highly homogeneous kneading, capability of a large volume introduction per batch, high productivity based on a short mixing time, and stable operation for each batch. According to a general structure of a closed type kneader, as will be described later, a pair of kneading rotors are disposed rotatably in opposed parallel relation to each other within a kneading chamber of a cylinder provided with heating or cooling means, and a material feed hopper having a forcing ram is provided at the top of the kneading chamber. One batch of material to be kneaded is introduced at a time from the hopper. The material is introduced into the kneading chamber by pull-in force (bite-in ability) induced by the rotors and the pressure of the forcing ram. When the entire material is completely forced into the kneading chamber by the ram there is started homogeneous kneading of the entire material due to rotation of the rotors. Therefore, it can be said that in such a kneader, completing the introduction of the material to be kneaded into the kneading chamber quickly and stably lead to shortening of the kneading time, improvement of the mixing performance and stable operation. On the other hand, as already known, closed type kneaders are broadly classified into non-intermeshing type (tangential type) kneaders wherein a pair of kneading rotors are not in mesh with each other, and intermeshing type kneaders wherein a pair of kneading rotors are in mesh with each other. Of the two types, the non-intermeshing type kneaders are generally known for permitting the introduction of a large volume of material and being superior in bite-in ability and high in their operability and stability. On the other hand, the intermeshing type kneaders are generally evaluated as being high in the additive dispersing ability and homogenizing ability. These are also already known. Needless to say, moreover, it is well known that various versions of each type of kneader are existent. For example, as to non-intermeshing type kneaders, the applicant in the present case has already filed Japanese Patent Application Nos. 927/84 and 184506/85, and as to intermeshing type kneaders, filed Japanese Utility Model Application No. 28833/71 and Patent Application Nos. 42083/74, 82005/78 and 106725/79.
Of the two types mentioned above, for intermeshing type kneaders, though their uniform additive dispersing ability and homogeneous kneading ability are high, it is generally difficult to introduce a large amount of material into the kneaders, and the bite-in ability is poor, so the operability and productivity are low; besides, unstable bite-in performance leads to an increase in the scatter of quality between batches, thus making production control difficult. The existence of such drawbacks common to intermeshing type kneaders is also a known fact. In this connection, the bite-in performance of an intermeshing type kneader and that of a non-intermeshing type kneader were compared using two laboratory apparatus. It turned out that the intermeshing type kneader exhibited a problem in its bite-in performance for the reason set forth below. One laboratory apparatus is a model kneader having an inside diameter of a kneading chamber of about 200 mm and an axial length shortened to 1/3 of the corresponding mixer (kneader), in which the material motion in the sectional direction of rotors can be observed through a glass window provided in a side face of the kneading chamber. The other laboratory apparatus is a model kneader having an inside diameter of a kneading chamber of 100 mm and an axial length same as that of the corresponding mixer (kneader), in which there are used rotors each constituted by a laminate of thin iron sheets. It is possible to set various blade arrangements and the kneading chamber is formed of a transparent resin to permit observation of the material motion in the interior.
In the non-intermeshing type, as shown in FIGS. 12, 14, 15 and 16, a pair of kneading rotors 10, 10 are rotatably disposed in parallel in non-intermeshing positions within a kneading chamber 6 formed in a cylinder 5, a hopper 7 provided with a forcing ram 8 is opened in the upper portion of the kneading chamber 6, and a door portion 9 is formed centrally of the bottom of the kneading chamber 6. As shown in FIG. 12, since the space of a communicating portion 11 at the center of the kneading chamber 6 is wide, the material fed from the hopper 7 and introduced under pressure by the forcing ram 8 is extremely easily introduced into the kneading chamber. Further, since there is a speed ratio (1.1.about.1.2) between the right and left rotors 10, 10, the action of pulling in a material 12 from the hopper 7 by both rotors 10, 10 is extremely strong, as shown in FIG. 14, at the time of a periodic synchronism (phase 0.degree.) of the tips of blades 10a, 10a which are formed axially twistedly on the peripheral surfaces of the right and left rotors 10, 10. This is also true when both rotors 10, 10 are 90.degree. out of phase with each other as shown in FIG. 15. Further, the flow of the material 12 from the rotor front to the back surfaces in the kneading chamber 6 and that from the rotor back to the front surfaces are effected smoothly and in an extremely well-balanced state. In the drawings, arrow P indicates a rotating direction of each of the right and left rotors; arrow P.sub.1 is an indicates the flow of the material 12; and 10a, 10b represent long and short blades formed on the peripheral surface of each rotor.
On the other hand, in the intermeshing type, as shown in FIGS. 13, 17 and 18, right and left rotors 10, 10 rotatably disposed in parallel and opposedly to each other within a kneading chamber 6 are in an intermeshing positional relation, so the inter-shaft distance of both rotors 10, 10 is relatively short as compared with that in the non-intermeshing type. Consequently, the space of a communicating portion 11 formed at the center of the kneading chamber is narrow, thus making it difficult for the material fed to enter the chamber, as is apparent from FIG. 13. In the intermeshing type, moreover, the right and left rotors 10, 10 are rotated at the same speed and their blades 10a, 10a are always 90% out of phase with each other as shown in FIG. 13, for preventing contact between the two. Moreover, each blade 10a is axially twisted as shown in FIG. 17, so the space from the hopper 7 to the door portion 9 is not fully opened at any time no matter in what state of phase both rotors 10, 10 are during their rotation, so that it becomes more difficult for the material to enter the kneading chamber.
Further, since the blades 10a, 10a of the right and left rotors 10, 10 are 90.degree. out of phase with each other and both rotors 10 rotate in directions opposite to each other as indicated by arrow P, the material 12 which has been forced in from the hopper 7 through the forcing ram 8 is reciprocated from one rotor to the other rotor with a bouncing motion, as indicated by arrow P.sub.3. Thus, there was confirmed the problem that the material 12 merely reciprocated between the right and left rotors just under the hopper without creation of a strong material pulling-in action based on synchronism of both rotors 10, 10 as in the non-intermeshing type.